1. Field of the Invention
This invention relates to mixing and extruding of thermo-plastic and thermo-setting materials and to pelletizing thermo-set materials. More particularly, this invention concerns a screw or worm type apparatus or millstone extruder for the mixing and extruding of varied viscosity, natural and synthetic rubber and elastomeric material. Also the apparatus can be adapted for grinding thermo-set materials (scrap tires) into rubber pellets. Unless otherwise indicated the terms "extruder" and "extrusion apparatus" used herein, refer to and include a screw or worm type apparatus used to obtain an extrudate of desired cross-sectional configuration, and or for the mixing, blending, milling of thermo-plastic or thermo-setting compounds. The extrusion apparatus can also be used to grind thermo-set materials to pellets for reprocessing or to reclaim rubber.
2. Description of Prior Art
The now conventional transfer type extruders, includes a barrel, a screw type rotor within the barrel which is adapted for rotational movement relative to the barrel and a means of introducing the material to be processed into the extruder, such as a hopper and its associated apparatus, if any. The rotor is provided with various threaded configurations and rotational movement forces the material through the barrel and out of the down stream end of the extruder. Interposed between the hopper and discharge end are multiple rotor to barrel to rotor stock transfers which cross blend the process material passing from rotor to barrel to rotor. Thus, while the process material is being discharged from the extruder, hot or cold unprocessed material is fed into the feed hopper at the opposite end of the extruder to provide a continuous extrusion process.
Examples of the prior art are my U.S. patents including U.S. Pat. No. 2,744,287 dated May 8, 1956; U.S. Pat. No. 3,375,549 dated Feb. 2, 1968; U.S. Pat. No. 4,075,712 dated Feb. 21, 1978; U.S. Pat. No. 4,872,761 dated Oct. 10, 1989; and U.S. Pat. No. 4,944,597 dated Jul. 21, 1990.
Although many problems relative to the extrusion of plastic materials have been solved temperature stratification, longitudinal blending, adaptability to a wide range of compounds and temperature control are continuing problems.